Rock climbing footwear is specifically constructed for rock climbing in outdoor environments and indoor climbing facilities. Rock climbing footwear is typically composed of three basic components: an upper, an outsole and a mid-sole. By design, all three of these components give rock climbing shoes their distinctive performance characteristics.
The upper of a rock climbing shoe is typically composed of leather, a synthetic material, or a combination of both. The upper provides an abrasion-resistant protective covering for the dorsal surface of the foot. The upper of the shoe has either elastic stretch panels or a lacing system to secure the footwear on the foot. In the heel area, pull tabs are often added to the upper to help pull the shoe onto the foot.
Rock climbing footwear typically has low interior volume and therefore a foot-conforming or snug fit. To provide dimensional stability to the upper, a lining material is often laminated to the upper. The lining can increase user comfort by limiting stretch of the upper, managing foot perspiration during periods of activity, and offering a degree of insulation.
The outsole of the rock climbing shoe is the plantar section of the shoe which contacts the ground when the climber walks. It is typically, but not always, devoid of tread patterns. Outsoles are made with special rubber compounds with high friction properties that enable the climber to adhere to climbing surfaces.
The midsole of a rock climbing shoe is laminated between the upper and outsole. The physical properties of a midsole affect the performance of a shoe. The thinner and more flexible the midsole, the greater the proprioception between the climber and the climbing surface. Additionally, a thin, flexible midsole increases the contact surface between the outsole and the climbing surface, maximizing the shoe's adhesion to the climbing surface.
A thin outsole compliments a thin midsole for climbing on small surface features. Soft and flexible synergistic upper, midsole and outsole designs allow a shoe's rubber outsole better conformation to the climbing surface.
In other climbing situations, a thicker, longer and less flexible midsole is desirable. In such cases, more of the climber's weight is transferred to the lateral and medial edges of the shoe, thereby decreasing his or her fatigue by shifting the work to the larger musculoskeletal groups of the legs. This increases efficiency when forefoot edge contact or edging is utilized, advantageous when climbing cracks or minute ledges. Firmer, less flexible overall designs are generally better for all-day climbing, walking comfort and crack climbing environments.
To provide additional climbing performance, rubber overlays or rands are applied over and around the forefoot and rearfoot areas of the shoe. The rand is made from a high-friction rubber, similar to the outsole material, providing greater adhesion to a variety of climbing surfaces. The rand provides additional structural support to the upper, a more secure fit and abrasion resistance.
A forefoot rand gives the climber additional purchase when using the upper's sides or dorsal area for climbing features such as cracks, in which the outsole of the shoe has little contact with the climbing surface. A rearfoot rand has an additional performance function in applying tension to the Achilles' tendon and arch area of the foot, further securing the shoe to the foot. Putting tension on the Achilles' tendon allows the climber to use techniques such as the heel hook, a means of pulling with the posterior portion of the climber's heel. A rearfoot rand can also tension the foot within the forefoot of the shoe, thereby concentrating more force on the great toes.
Currently, sheet or roll stock of high friction rubber of uniform thickness is used to produce rands for the climbing shoe manufacturing process. This high friction rubber is laid out on a cutting table or on a heavy die cutting mechanical press table and cut manually or mechanically with metal dies designed for the style and function of the shoe being produced. This step is labor intensive as the worker has to align the cutting die on the rubber to maximize rubber cutting yield yet avoid flaws that occasionally appear in the stock rubber.
Typically, the employee that performs this work is one of the highest paid workers on the assembly line because of the efficiency required and personal safety risk involved in the cutting process. Even though modern mechanical die cutting presses or clicker presses have incorporated safety systems, operators have accidentally lost parts of their hands while using clicker presses. Die cutting methods pose a constant safety risk regardless of the skill or attention of the worker.
Additional design or functional elements not already incorporated into the die can be added to the rand after the rand is die cut. Design or functional elements range from simple holes or ovals manually punched through the rand to more elaborate punches such as logographic marks or flex reliefs. Like the die cutting process, there is non-recyclable waste produced as well as additional labor required to complete this step.
After the climbing shoe upper is assembled and the last (the company's proprietary form in the anatomical shape and volume of a human foot taken transaxially and distally from the lateral malleolus) is inserted, the rand is ready to be bonded to the upper assembly. A heat-activated proprietary adhesive is applied to the upper and rand components. The upper and rand components are then pressed together for a specific time at a particular temperature. The remaining shoe construction steps, well known by those in the industry, are taken to complete the shoe assembly.
The assembled shoe is ready for finishing steps, one of which is grinding the rand and the outsole to match a given design and functional profile. Since the rand is cut from stock of uniform thickness, areas were the rand needs to be thinner are removed with an industrial grinding wheel. This process poses a number of hazards to the worker, such as accidental contact with the grinding wheel, inhalation of particulate and rubber dust, getting particulate rubber into the eyes, hearing loss due to elevated noise levels created by the grinder and, under certain environmental conditions, the possibility of explosion and fire caused by rubber dust suspended in the air.
To mitigate some of the worker safety issues, protective eyewear, personal noise reduction devices, respirators and protective clothing are available to or provided by the factory. To reduce the chance of explosion, vacuum dust recovery systems must be installed, serviced regularly and emptied as they fill with rubber compounds. All these steps require additional labor, expense and the willingness of both management and employees to adopt these measures.
The die cutting and grinding process also creates environmental problems. One by-product generated by this process is a waste stream of rubber that has no recyclable content, although it can be used as filler material in certain applications. However, the majority of waste rubber compound is disposed of in landfills.
Die cutting and grinding methods also consume considerable raw material and energy. Utilization of inefficient die cutting and grinding methods wastes a significant amount of high friction rubber, the most expensive component of the climbing shoe. High friction rubber is made from non-renewable, petrochemical-based components, the prices of which continue to increase.
Clearly there is a need in the industry to reduce exposure to workplace hazards, wasted productivity and greater high friction rubber yield in the production of climbing shoes, particularly in the production of the forefoot rand.